Papermaking machines are divided into three dewatering sections; the forming section, the press section, and the drying section. Each section employs a papermaking fabric.
The forming section receives a paper forming slurry of pulp which is approximately only 0.5% solid material. The slurry is delivered on to a forming fabric which acts to drain the water from the slurry to a point that the solid content is increased to between 18% and 23%, and slurry of pulp is formed into a sheet.
The press section receives the sheet of pulp onto a press fabric, which in cooperation with press rolls, further drains the water to increase the solid content of the sheet of pulp to between 36% and 44%.
The dryer section receives the sheet of pulp from the press section onto a dryer fabric which carries it through the section. The dryer fabric also serves as a backing medium to press the pulp sheet against heated cylinders which achieve the desired dryness.
The use of chlorine and other oxidation agents in the papermaking process has proven to be problematic because these chemicals deteriorate the forming materials of the papermaking fabrics. Attempts have been made to improve the chemical resistance of papermaking fabrics with the selection of various synthetic materials and various fabric forming techniques and structures. The one constant that always remained was that the materials forming the press fabric having the desired strength, durability, and elasticity quality did not have the chlorine resistance qualities.
U.S. Pat. No. 4,973,512 is an example of such an attempt. The patent discloses using polybutylene terephthalate filaments (PBT) to form the base fabric. This product contains some physical properties similar to nylon and, at the same time, has a high degree of resistance to chlorine. The fiber batt used with the base fabric is composed of polyethylene terephthalate (PET) which does not possess the physical properties of nylon. The resultant felt therefore exhibits an adequate chemical resistance to chlorine, but has inferior physical properties in comparison to nylon felts.
It is an object of this invention to produce a papermaking press fabric which overcomes the disadvantages of the prior art as indicated above.
It is another object of the invention to provide a papermaking press felt having the elasticity characteristics and wearability of nylon so that the fabric will have superior runnability on the paper machine.
Another object of the invention is to produce a papermaking press fabric having equal physical and chemical resistant properties in both its base fabric and its fiber batt which is secured to the base fabric.
It is an object of the invention to produce a chlorine resistant papermaking fabric in which the base fabric has sufficient elasticity to allow the needling of fiber batts thereto with a minimum fiber and yarn damages.